Field of the Invention
The invention relates to an electromagnetic wave heater for heating objects, and more particularly to an electromagnetic wave heater for burning up or drying industrial wastes such as uncooked foods and plastics.
Description of the Related Art
Microwave heaters have been widely used in various industries and household microwave ovens. Electromagnetic wave or microwave heaters heats an object up by subjecting a large dielectric loss material such as water to an electromagnetic wave or a microwave to cause a heat generation proportional to an amount of the dielectric loss. A typical one of the microwave heaters is illustrated in FIG. 1 in which the heater comprises an electromagnetic wave generator 1, a waveguide 2 and an applicator 7. The applicator 7 accommodates a turn table 8 on which an object 4 to be heated is placed. The wave-guide 2 connects between the electromagnetic wave generator 1 and the applicator 7 to guide the electromagnetic wave or microwave generated by the generator 1 into the applicator to thereby permitting the electromagnetic wave or microwave to be applied on the object 4 placed on the turn table during which the turn table is kept in turning or rotation.
The wave-guide 2 is connected on a top or side face of the applicator 7 to permit the microwave to irradiate on the object. The applicator 7 has a metal inside wall by which the microwave tends to be reflected irregularly so that the reflected microwave irradiates symmetrically on the object in various directions. As a result, the microwave is not sufficiently absorbed by the object but reflected thereby. The reflective ratio of the microwave by the object depends upon the shape and size of the object. Actually, approximately a half of the microwave output power may contribute to heat up the object.
To improve the efficiency of the heating up of the object, it was proposed that the applicator 7 was designed to form a resonator as illustrated in FIG. 2. Such technical idea is disclosed in the Japanese Patent Publication No. 56-54548. In this case, the dielectric constant is variable by changes of temperature of the object to be heated up and a cap thereof. For that reason, an impedance adjuster 9 is provided between an electric wave generator 1 and the applicator 7 so that a microwave generated by the generator 1 is adjusted by the adjuster 9 to follow the change of the dielectric constant of the object to keep the optimization of the resonant state in the applicator 7.
The above resonant type of the applicator requires that a power monitor is provided in the wave guide for guiding the microwave to monitor both an incident wave and a reflected wave so that a tuning of a adjuster rod is made to keep a smallest amount of the reflected wave. To achieve the above, it is required to provide a power monitor, an adjusting and moving device and a control system for controlling the same. Introduction of such system may result in an expensive heating system, for which reason it is preferable that the microwave heater has no complicated system to result in a large cost thereof.